This invention generally relates to the field of chemical laboratory equipment for sample preparation and particularly to the use of a hydrophobic membrane to separate water from an organic solvent, and more particularly to an apparatus and method for increasing the flow rate of the solvent through the membrane without adversely affecting the performance of the membrane.
When samples are to be analyzed for organic and/or inorganic trace compounds, the samples are typically extracted with an organic solvent. The solvent extracts the compounds from the sample, due to selective chemistry.
Before the extract can be analyzed, all residual water should preferably be removed from the extracting solvent. This is due to the adverse effect residual water can have on the analytical instruments that are used to analyze the sample.
Current practice embodies the use of a drying agent called sodium sulfate and has been the standard technique to remove the residual water from solvent extracts. Sodium sulfate is a granular material that has a high binding capacity for residual water. The sodium sulfate is first heated to drive off any water that has been adsorbed into the material. This typically requires heating overnight at 400 C. The sodium sulfate is then placed into a glass funnel containing filter paper, or a chromatography column. The funnel or column is then washed with extracting solvent to wash off any impurities. The extracting solvent is then discarded. Once the sodium sulfate is clean, the solvent extract is poured on top of the sodium sulfate. As the solvent drains slowly through, the residual water becomes bound to the surface of the sodium sulfate. The collected solvent passing through is now dry and ready for analysis.
The use of sodium sulfate, even though easy to use, requires many physical manipulations. Sodium sulfate requires the use of glassware that must be subsequently washed so as not to introduce contaminants into the samples and requires the purchase of, and the disposal of, the used sodium sulfate. The labor time and the materials costs, add significantly to the total cost of performing sample extractions.
U.S. Pat. No. 5,268,150 assigned to Corning Incorporated, discloses the use of a hydrophobic membrane in an extraction device which allows a solvent to pass therethrough, yet will not allow a significant amount of water from the sample liquid to pass therethrough. The patent discloses that hydrophobic membranes incorporating polytetrafluoroethylene (PTFE) have been found to be very effective in achieving the desired results of letting solvent pass, while retaining the sample usually consisting of a relatively large portion of water or an aqueous solution. The patent goes on to state that the typical dimensions of the membrane range from 10 to 50 millimeters in diameter with a thickness ranging from 0.1 to 5.0 microns with a pore size ranging from 0.2 to 5.0 microns, depending upon the sample being processed. In addition, this patent emphasizes that the extractor design disclosed therein includes a chamber specifically for loading sodium sulfate to assist in water removal.
Attention is also directed to the following U.S. Pat. Nos. 3,953,566; 4,187,390; 4,909,810; 5,792,425; 5,454,951; 5,976,380 and 6,019,920.
Accordingly, it is an object of the invention to improve on the above referenced designs and provide a more efficient technique for separation water from a given solvent. More specifically, it is an object of the present invention to provide a method and apparatus and improved membrane design to improve the purification flow rate of a solvent/water mixture or emulsion through said membrane, to remove water, without adversely effecting membrane performance.
A method for separating residual water from a solvent, comprising the steps of providing a reservoir containing a solution comprising solvent containing residual water, the reservoir having an opening to allow the solution to drain from the reservoir, resisting the flow of the solution from the reservoir with a membrane layer comprising a layer of fluropolymer material, said membrane material having a IPA Bubble Point of xe2x89xa725 psi, said membrane positioned in the series with the reservoir opening, decreasing the pressure on the second side of said supported membrane relative to the first side of said supported membrane to thereby increase the flow rate of the solvent through the membrane and therein removing said water from said solvent to provide a solvent with a water level of less than or equal to 1.0 ppm.